(1) Field of the Invention
The present invention relates to sealed batteries. In particular, the invention relates to a technology for manufacturing a battery where a closure cap is provided in an opening in the external battery casing, with an injection hole provided in the closure cap to allow the injection of electrolyte being sealed using a sealing plug.
(2) Related Art
In recent years, sealed batteries have been widely used as a power source in portable electronic appliances such as mobile telephones, audio-video devices, and computers. Representative sealed batteries include alkaline batteries, such as nickel-hydrogen storage batteries and nickel cadmium storage batteries, and lithium-ion batteries.
Both cylindrical and rectangular sealed batteries are widely used, with rectangular batteries being subject to special attention due to their superior space-saving potential when used in portable devices.
Sealed batteries are constructed as follows. A generator element is formed by impregnating a set of positive and negative electrodes with an electrolyte. This generator element is placed inside an external casing composed of a metal cylinder. An opening in the metal casing is sealed using a closure cap, with the edges of the closure cap and the metal casing being hermetically sealed to prevent the leakage of electrolyte or gas. This seal is often formed by a mechanical calking method, though in the case of rectangular sealed batteries, laser welding is also commonly used.
As part of the manufacturing, the set of electrodes needs to be impregnated with the electrolyte. One common method of doing so inserts the electrode group into the metal casing before injecting electrolyte into the metal casing and sealing the battery with a closure cap. However, when the seal between the closure cap and the edges of the opening in the external casing is formed using laser welding, there are many cases where a proper seal cannot be formed due to electrolyte adhering to the parts subjected to welding.
In view of this problem, Japanese Laid-Open Patent Application No. H11-025936 teaches the following technology. A small injection hole, with a diameter in the region of 1-2 mm, is formed in the closure cap to allow electrolyte to be injected into the battery. The opening in the metal casing is first sealed using the closure cap before the electrolyte is injected into the injection hole using a nozzle. After this, the injection hole is sealed using a sealing plug which is laser welded to the closure cap to seal the battery.
With the above method, the closure cap is laser welded over the opening in the external casing before the electrolyte is injected into the battery, so that there are no imperfections in the seal due to electrolyte adhering to the welded parts. However, there is still the possibility of the electrolyte adhering to the sealing plug that is used to fill the injection hole. When laser welding the sealing plug to the closure cap, the welding needs to precisely follow the external circumference of the sealing plug. However, if electrolyte adheres to the edge of the injection hole, spattering will occur during welding, causing imperfections in the weld. This is a common problem.
In keeping with the small size of the injection hole, the sealing plug that seals the injection hole needs to be minute, which makes the plug difficult to handle and to insert into the injection hole during manufacturing. This also constitutes a problem for battery manufacturers.
It is a primary object of the present invention to provide a technique which, in the manufacture of sealed batteries, (a) reduces the occurrence of defective seals for an injection hole provided in a closure cap during and (b) facilitates the sealing process.
In order to achieve the stated object, the present invention forms a sealing plug for sealing an injection hole provided in the closure cap of a sealed battery from a support member and a plugging member. The support member is fixed on a surface of the closure cap so as to cover the injection hole. The plugging member is at least partially formed of an elastic material and is supported by the support member so as to plug the injection hole.
When an injection hole is sealed using this kind of sealed plug, the elastic plugging member of the sealing plug is supported by the support member so as to plug the injection hole, forming an airtight seal. The support member is attached to the closure cap without the join between them needing to be airtight, so that batteries can be securely and easily sealed in this way.
When electrolyte adheres to the rim of the injection hole, this does not pose a problem to the process, such as welding, used to attach the support member to the closure cap.
This means that the present invention does not suffer from defective seals, even when electrolyte is present at the rim of the injection hole.
While the plugging member of present sealing plug can be made small in accordance with the size of the injection hole, the support member can be made quite large to facilitate the handling of the sealing plug. As a result, misalignments of the sealing plug with the injection hole during manufacturing can also be avoided.
The present sealing plug may use a flat plate as a support member, to which an elastic material can be applied to form the plugging member. This makes the sealing plug relatively easy to manufacture.
The width of the base part of the plugging member can be made larger than the diameter of the injection hole to securely seal the part. When doing so, it is preferable to form a recess in the closure cap around the injection hole to accommodate the base part of the plugging member.
The support member can be easily attached to the closure cap by forming the outer edges of the support member so as to reach the edges of the closure cap. This enables the edges of the support member to be welded to the edges of the closure cap.
More preferably, the outer edges of the closure cap will be turned up so as to facilitate welding of the edges to the edges of the support member.